The present invention relates generally to an automotive suspension system with variable damping characteristics providing both driving stability and riding comfort. More specifically, the invention relates to a system controlling the variable damping characteristics of an automotive suspension system such that the damping forces against bounding and/or rebounding will not serve to amplify vibrations at least of the sprung mass.
Japanese Patent First Publication No. (Tokkai Sho.) 50-83922, published on July 7, 1980, discloses an electronically controlled automotive suspension system. In the disclosed system, the relative displacement between the sprung mass and the unsprung mass and the acceleration of the sprung mass are detected. Based on the detected relative displacement, a reference value for the sprung mass acceleration is derived for comparison with the detected acceleration value. Control is performed to minimize the difference between the detected acceleration value and the reference value so as to improve riding comfort.
In such conventional suspension control systems, the reference value derived on the basis of the relative displacement of the sprung mass and unsprung mass has to be small enough as to ensure good riding comfort. This, on the other hand, results in an excessively soft suspension, which degrades shock absorbing ability and thus results in reduced driving stability.
Consequently, although the prior proposed suspension control system may improve riding comfort to a certain extent, it does not satisfy the requirement for the better riding comfort while ensuring good driving stability.